Nickel-iron alloys



States vs'mexncmorz ALLOYS "'Cliarles Alfretl' Clark? Edgbaston, -Birrningham,England,

' 'assignor" to' 'l he lnte'rnational Nickel Company, Inc.,,

"New York, *N.Y.,za corporation of Delaware N6 Drawing. 'ApplicatioriMai-ch 12,1958 IS'er-i'al N0. 720,807

' Claims'-'pr"loi ity application GreatBritain March13,:19'57 920mm. 1C1; 75-123 imaking :indicating instruments, such as magnetic: speed iometers almost?- eornpletely independent of variations- 'in etemperaturesover;aneunusually wide range of tempera- 'tures. -rTheseealloys generally: contain about 29% to about 31% nickel and usually much smaller amountsx of chromium. They. also always contain small amounts of carbon and silicon/The alloys possess a negative temperature coeflicie'ntof'magnetic permeability that is sub- -stantially*.consta-nt over a rangeofutemperature below the G1irie-point; rthis range usually-beingof the'o-rder of 1 80" F. Thermartensitic -ttransformationtemperature, i.e., the

:temperature -at which sthereis .7 a phase change from :t-ga'mma toalpha maybe within or below this range. In I practice; the spccificationsrof: such alloys require a given Curie temperature randealow martensitic v transformation rtemperature. V v

However; inathe manufacture-of= these alloys considrerable difiicultywis-l encounteredainproducing alloys of '-tconsistent-;properties,- that is 1 to' say, the" Curie point variesconsiderably:from oneheat toanother, so that an '2 alloywhichtshouldmeet-the required specification fails to ';do so. -Mo-reover thezrnartensitictransformation temperature oftenwaries. fromwheat to heat. 'When the ztriansformation:temperature "exceeds -..that-required-by a :partic-ulan specification; the desiredhigh permea-bility of 'lthe'falloys '.-at= low-temperatures is irreversibly reduced when- --the alloyis inadvertentlycooled; during service, t'ibSlOW: theumartensitict transformation temperature .thus

.? jinpairingdhe, effectiveness of the P measuring instrument; wIn .a'ccordancerrwith thezpresent invention it has now -7been found that the-irregularities. in the properties of .the

1alloys'heretofore--employed are-largelycaused byvariations in-fthe carbon and silicon contents, r particularly in the-former. Carbon has :commonlywbeen :regarded'as an -element1necessaril'y present and harmless in amounts up to,=- say,0.25-%. fil-ndeedithe carbon content ofthe. alloys -gnormally usedaisrabout 0.2%;thou-gh it. mayvaryafrom athimbyv amounts whichrhave; been consideredv negligible butwhichearesin'factaimportant. The silicon content of -t t-her ;alloysihas also-=comrnonlyabeenabout 0.2%.

having-.-.discoveredtheirnportanceof minor vari- I heecarbon and -asilicon-contents of the aforedescribed :pricprsvart,v alloys to .minimize these war-rations Mand overcomes the disadvantagescaused .lthereby are, in practice tdiffic'ult The-carbon content, as. will be appreciated by those,..sRi1lecl..-in lthesarn isl difiicult .to control i within narrowwlimits} particularly vit the alloydsmade by smelting lfwlther carbon. content isflmerelysrreduced the martensit cq transformation temperature is raised,- so. that the alloy irreversibly loses its high permeability if exr Patented ,Mar. 29, 1960 ,posed' ame low. .temper aturesfltor which ,it .is. often liable t .to be subjected .in .use. valfniritturn'the proportion; of iron is reduced, in order/once more to. lower ilthe= transformation temperature, the proportion ofnickel isautomatical- W ly increased, which causes anincrease of :the Curiepoint, Y,

with the result that the requirements of manyaspecifica tions are unsatisfied. v I

Although attemptswere made: to overcome-theforegoing difliculties r and other :disadvantages, none, as far as. I amaware, was:entirely successful when carried into r practice commercially on an 1 industrial scale.

.It hasnow. been discovered lthatthe aforementioned transformation stemperature can be maintained at a desired'lowdevel andathe, Curie, point. can be controlled in special iron-nickelralloys' which contain certain amounts of at least one element: selectedlfrom-the group consisting of copper and molybdenum. v p

,.measuring or indicating instruments which" are-substan- .lt-risan object of the present invention -to provide .tially independent of temperature variation.

it Another object of the present: invention is to provide measuring I or indicating instruments "whichqmaintain i 'a high degreeaof accuracy -when subjecteding serviceto temperature variation over a wide:1'ange. of temperature. Elie-invention also contemplates providingfor ruselin measuring :instruments 1 temperature responsive..- elements a comprised of *alloys:v of special -composition which-w are capablesofconsistently meeting-the; properties'vrequired by, specification standards.

1 It is afurther object oftthe. invention ltotprovide special iron nickeh alloysfor-.:-use as trtemperature acompensating a elements; the alloys being of such:icomPositiore-that: -.the

- martensitic transformation temperature thereofizcan'abei t maintained ata desired-t-lowvlevelz and' the Curie p'oint; thereof can; be: controlled "SO/that'- the requirementspof specification standards can be,consistently:satisfied. I

rItisanotherohjject ofithe invention-to providela process a foraaccomplishing the foregoing; objects.

from the following description. Generally,;speakiug,zthey presentrinvenHort-contemplates -;Other objectsandsadvantages will become: apparent v:prov-idingspecial :iro n' -nickel alloysvforsuseeas temperature compensatingwelementsaain: magnetic measuringiior r indicating instruments :such that-.itheillatter operate almost orwsubstantially completelyindependently of :temperature changes over a wide erange .of-temperatures. .iThe: alloys of the present 1 invention: are substantially; freexofl carbon and silicon and containabout;28.4%2'101'about.x32.5;%

nickel; at least one element selected fromrthe groupjconsisting of copper-and molybdenum,:the' ba-lan'cejofz the alloys being essenti'allywiron. Manganese cam alsoa'be V prresent-tin-ithe alljoys. .The -copperwand/or.moiybdenum and any manganesemust be presenfinamounts suchitIiat' the relationship expressed by the .following--'formula: is satisfied: 7

" 2 percent Cu+ 1 .2 Xpercent -Mo +2 X-percent Mn L2 to 12 I Notmore than up to copper, up 10' l 0% molybdenum and,'if employed,i-up.to 6% manganese can betpresentt-in the alloys oftheinventionuandthe relationship setrforth hereinabove must be satisfied; When the a lloys; contain but one l'elementfselejcteclfrom.the ,g'rouptQconsisting of copper 'and molybdenum; the'respective ramountsrforreach of'the'se elements are 0.6%. :to copper an d.Y"1l%,-1to 10%rnolybdenum. ltis particularly 'i'r'nportant thatthe relationship established by the above formula be observed 1 to achiever/highly -'s'atisfactory results; For eXample, if

the value obtained employing the formula exceeds the' upper limit represented by the number 12, the all'oys tend to 'becomehard -and brittle during processing due to the production of second phases. This in turnwould 3 lead to a reduced degree of compensation and variable results between different batches of the same alloy.

It is advantageous in obtaining highly satisfactory results that the alloys contain 29% to 31% nickel and contain copper and/or molybdenum and any manganese in such amounts that the foregoing formula gives a value between about 4 and 9. When this relationship is observed, a Curie temperature of, for example, 180 F. and a martensitic transformation temperature of less than 80 F. and even down to less than -200 F. can be realized. However, in applications requiring relatively high Curie temperatures, e.g., above about 250 F., operating in the lower end of the range of the relationship set forth hereinbefore, e.g., 1.2 to about 2, gives satisfactory results particularly where nickel contents in the upper end of the nickel range are employed. Such alloys are stable down to at least 80 F. Copper and molybdenum and also manganese serve to reduce the transformation temperature, and variations in the proportions of them produce variations in the Curie point which are much smaller than those brought about by carbon and silicon. As a result thereof, the martensitic transformation temperature can be maintained at a desirably low level, e.g., as low as about -200 F. and the Curie point thereof can without appreciable difficulty be controlled. Thus, the alloys of the present invention overcome the inherent disadvantages of prior art alloys which, because of varying carbon and silicon contents from heat to heat, manifested inconsistent properties, whereby their effectiveness as compensating elements was seriously impaired. By reason of having a balanced composition the alloys of the present invention thus possess stability, i.e., do not undergo change of phase or an irreversible change of magnetic properties, at temperatures as low as 80 F. and as high as 400 F. and are therefore eminently suitable for use in indicating or measuring instruments which may experience very low and very high temperatures, such as aircraft instruments and outdoor domestic electrical supply meters.

As indicated hereinbefore, the nickel content of the alloys is from 28.4% to 32.5%. Nickel in excess of 32.5% leads to a more expensive final product because of raw material cost and also gives rise to an alloy possessing a smaller temperature range of compensation. On the other hand, when the nickel content falls below 28.4% the permeability is reduced so that more of the alloy is required to obtain a given degree of compensation. In addition, if the nickel content is reduced much below 28.4%, it becomes impossible to maintain the martensitic transformation temperature below 80 F. and at the same time keep the Curie temperature at a reasonable value, say 180 F.

The alloys are free or substantially free of carbon and silicon. In any event, the carbon and silicon contents should each be not more than 0.03% and preferably less. The use of chromium in the alloys should be avoided and, if present, chromium should not be present in amounts greater than 0.2%.

In obtaining the most consistent results, alloys containing molybdenum and/or copper are made by powder metallurgical methods. vIf the alloys contain manganese, they should be prepared by melting under an inert atmosphere. Manganese oxidizes so easily that it is diflicult to control the amount to be found in the final alloy, and it reduces the corrosion-resistance of the alloy.

It has been further found in accordance with the invention, that the Curie temperature and the transformation temperature 6 at which the austenite transforms on cooling, are given approximately by the equations:

6 =A +70 Ni-48 Mn--22 Mo+40 Cu and 0 =A 54 Ni-90 Mn-36 Mrs-3,6 C 1 (As used herein and in the appended claims, the tern peratures 0 and 0 are given in degrees Fahrenheit.)

The values of the constants A and A in these equations depend on the amounts of incidental impurities arising from the source of raw materials and method of production. The constants can thus be determined for a particular method of production and the coefficients for nickel, manganese, molybdenum and copper will then enable any alloy to be made to a required specification.

Since the equations for the temperatures contain four variables in the contents of the elements there is clearly a range of alloys which will possess any particular set of values for 0,, and 0 Other considerations such as corrosion-resistance, cost and availability of raw materials can thus be used to fix the final composition of the alloy. Using one powder metallurgical method it was found that the constants A and A; were 1900 and 1580, respectively. If, therefore, it is desired to manufacture an alloy for which 0 and 0 equalled 140 F. and 160 F., respectively, the equations can be rewritten:

140= 1900-|-70 Ni-48 Mil-22 Mo+40 Cu and l60=l58054 Ni-90 Mn36 Mo-36 Cu Assuming that fairly good corrosion-resistance is required, it is desirable to have a fairly high molybdenum content, say 3%, and no manganese. Substitution in the fore going equations leads to two simultaneousequations as follows: it

70 Ni+40 Cu=2106 54 Ni+36 Cu=1632 is not desirable to reduce the nickel content below 28.4%,

however, as the constants would-ndlonger remain the same, even for a given method of production. Inaddition, the permeability at a given temperature would tend to be reduced. Heat treatment is required to render the alloy austenitic, but provided the cooling rate is not very slow, e.g., longer than six hours to cool to 200 C., the heat treatment is not cfitical.

In carrying the method aspect of the invention into practice in producing a suitable iron-nickel'temperature compensation alloy having a specified Curie temperature and martensitic transformation temperature, a reference alloy substantially free of carbon and silicon is prepared by the same method and using the same raw materials as to be used in the production of the iron-nickel compensation alloy. The nickel content of i the reference alloy is from 28.4% to 32.5%, the balance of the alloy being iron. Up to 6% copper and/or up to 10% molybdenum and, if used, up to 6% manganese can be present in the alloy. The Curie temperature and martensitic transformation temperature of the alloy are then determined in the usual manner. Having determined the Curie and martensitic transformation temperatures, the

constants A and A in the equations for 0,, and 0,, above are determined, the values for Ni, Mn, Mo, and Cu in the equations being the respective amounts of these elements in the reference alloy. The determined constants A and A together with the specified Curie temperature, 0 and martensitic transformation temperature, 9 are then substituted in the equations referred to hereinabove. An iron-nickel temperature compensation alloy is then prepared having a nickel content, a copper and/or molybdenum content and, if present, a manganese content which satisfy each of the equations having assures the specified 'urie andj martensitictransformation tem; peratures and determined,.constantsaAm ands-A ffi rser herelationship expressed by the formula must. also .be. satisfied... I

Asuitable. powder; metallurgicaLmethod of: preparing alloys in.- accordance, with. theinventiomis :described in connection with an alloy containing'molybdenum..aud copper. inaddition to. iron .and nickel... Pure raw materials of.,, the constituent. elemelltswere. .usedt follows; carbony}, iron: powden, grade MOB, having,; a.-mean.partiele sizeofiabout microns;,carhonyl. nickeLpowden, grade. A having a mean.particle;size.of .aboutrinmicrfins; 9 .0: trolytic copper, powder- 30Q mesh,. having. a.mea1 u par-v ticle,v size: of less than. 5,0...mic'rons,3 and hydrogemreduced molybdenurnrpowder having amean purfifile. size. 0f.- about 5;. microns. Suitable. weights. of; each. of. these powders were mixed in,,a...cone-mixer..for. about. 1, hour and this. intimate. mixture of powderswas then ..compacted intota' billet of approximate. dimensionslQ. 1.2 /2 X11! ata pressure of 50 tons/sq. inch. The billet was then sintered in hydrogenv for 4;,hours: at-6003 C. to remove residual oxygen. andJcar-bon andifinallyqfor-b hours-.at 1250 C. to produce homogenizationof the alloy. The final alloy billet was thenworked-byconventional forg; ing and" rolling operations with frequent; high temperature animals to stripiof suitable, thickness for the manufacture of shunts for electrical" instruments;v

By usingthe foregoing powder metallurgy; technique, in" which the alloy doesnot become moltem the need for deoxidants such,asmagnesium;titanium etc, is avoid-i ed and"-there is, no-pick, up ofimpurities from furnace linings, evaporation" of*constituentelements; etc. Thus, the final product can be muchimore. closely. controlled as: regardschemical composition,; simply by careful weighing out of the constituent powders at the begin ningof the process. While it is preferred to use powder metallurgymethodsin preparing the alloys of the pres;

entinvention, vacuum melting tech'niques may be suitably employed particularly where facilities for production by powder metallurgical techniques are unavailable;

As will bereadily-uuderstoodbwthose skilled in the. art, the expression balance-- used. in, referring to the iron content of the, alloys. of the-invention. does not ex,- clude the. presence of otherv elements commonly present in such alloys as incidental elements, e.g., deoxidizing and .cleansing. elements, and; impuritiesordinarily -associatedtherewith'in small amounts whlchidomot adversely affect. the basic'characteristicsof-t-he;alloy.s. If, however,- close control ofproperties is -required; a method of production wouldhave tobeyusedysuch as powder metal lurgy or vacuum melting methods, whereby such: im. pulity levels could be maintained at: allow-level and-fur thermore 'so that composition of the alloy can be accurately predictedlfrom 'thebweights of: the: initial raw materials.

It is to be observed that the present inyentionprovides temperature compensation elements r0 11; use snaking the -alloysof thepresent inventipn -are-highly suitabie for use in magnetic speedometers -watehounmetersg volts age and current regulatorsand,.othen, electrical; supply meters...

Although the present invention has, been described in conjunctiongwith preferred embodiments; it is to be understood "thatmodifications and variations' may be resortedto-withorit departing from the spirit and scope of theinvention; asthose'skill'ed -in the art will1readily understand; Such modificationsand variations are consid-' ered to be within the purview, and scope of the invention and appended claims.

1. A temperature, responsive elementforusein mag: netic indicating instruments; subjected in service to changes in temperature overnazwide range 'of; temperature comprised of-a temperature compensating alloy char acterized by the propertypof, haYin -;Specified Curietom perature, and-martensitictransformation temperature, said compensatingalloy being substantially free of carbon and silicon, and, containing:28.4%f' to 3215j% ,"nie l iel, at least one metal selected from the group consisting of {copper and molybdenum in amounts of; up to 6% copper and up to. 10% molybdenum, upto. 6% manganese, and the balance being substantially iron, the niqkelfand' metal'from the group consisting of copper and" molybdenum, and,

the manganese'being "present in such amounts as to satisfy the relationshipexpressed by the-formula I 2 Xpercent Cu+ 1.2 percent percent Mo .+2- percent Mn= 1.21012 andto satisfyeach" of the following equations; 0

whereinA andfA are-constantsfandv and 0 ,,a1je-vv e. pec fi d: Curie tempe uremart m tiet aee o mation emperat e, especti y- 2-" A. empe a we omp nsa n loy tor usez a netic measuring I instruments subjected in set vice to ternperature changes comprising up to but not more than 2 percent Cu+:1.2 Xpercent Mo 7 +2 XpercentMn: 1.2 to 12 said:..alloy -bei ng -..further characterized -by -being capable of meeting-a specified Curie,tempenatureand; martensitic transformation temperature, when:the=same-amountsof nickel copper, molybdenum and manganese. are so.cor-- indicating 011 measuring-instruments-substantially inde- I pendent of variation in--temperature"over a wide range of temperature. Not only do the compensation elements of the present invention afford the attainment of accurate results, but accurate results are obtained consistently. No detrimental deviation from a predetermined and required Curie temperature is incurred from one heat to another of the alloys of the present invention. This latter characteristic overcomes a serious drawback of prior art alloys. Test-checking of the alloys to determine the properties thereof is not required in accordance with the present invention. Moreover, desired low martensitic transformation temperatures can be easily achieved in accordance with the invention.

The temperature compensation elements comprised of related that eachzof; thefollowingequations are satisfied:

wherein A and A are constants and 0 and 0 are the specified Curie temperature and martensitic transformation temperature, respectively.

3. A temperature responsive element capable of compen-sating for errors in the readings of magnetic measuring instruments when subjected to temperature variation durlng service, said temperature responsive element comprising a compensating alloy containing 29% to 31% nickel, not more than 0.03 carbon, not more than 0.03

molybdenum and manganese satisfying the relationship expressed by the formula ZXpercent Cu+1.2 percent Mo v v +2 percent Mn=4 to 9 2X percent Cu+1.2 percent Mo 1 +2 percent Mn=1.2 to 12 and the balance of the alloy being substantially iron.

5. A temperature responsive element as described in claim 4 wherein the metal selected from the group consisting of copper and molybdenum is copper.

, 6. A temperature responsive element as described in claim 4 wherein the metal selected from the group consisting of copper and molybdenum is molybdenum.

7. A temperature responsive element as described in claim 4 wherein'both copper and molybdenum are present in the alloy. 8. A method for producing a magnetic iron-nickel temperature compensation alloy having a specified and pre-required Curie temperatureand martensitic transfor mation temperature comprising the steps of establishing a reference alloy composition substantially free of carbon and silicon and containing 28.4% to 32.5% nickel, up to 6% manganese, up to 10% molybdenum, up .to 6% copper, and the balance essentially iron, the amounts of nickel, manganese, molybdenum and copper in said reference alloy composition being within their respective ranges such that the relationships expressed by the following equations:

(l) A =6,,70 Ni+48 Mn+22 Mo-40 Cu (2) A +54 Ni+90 Mn+36 Mo+36 Cu aresatisfied, 0 and 0,, being the Curie temperature and martensitic transformation temperature, respectively, of said reference alloy composition and A and A being constants; and thereafter producing the iron-nickel temperature compensation alloy by the same method and wtih the same raw materials as employed in producing the reference alloy, said temperature compensation alloy being characterized in that it is substantially free of carbon and silicon and contains 28.4% to 32.5 nickel, and at least one metal selected from the group consisting of molybdenum and copper in the ranges of up to 3 A,=e,- Ni+48 Mn+22 Mo-40 Cu (5) 2 percentCu+L2 percent Mo 2 percentMn=1.2'to 12 are satisfied, 0,, and 0,, being the desired Curie temperature and martensitic transformation temperature, respectively, and A and A, being the constants of Equations 1 and 2 above, whereby there is provided a magnetic iron-nickel temperature compensation alloy having a speci and pre-required' Curie temperature and martensitic transformation temperature.

9. A method'for' producing a magnetic iron-nickel temperature compensation alloy having a specified and prerequired Curie temperature and martensitic transformation temperature comprising the steps of establishing a reference alloy composition containing up to about 0.03% carbon, up to about 0.03% silicon, 28.4% to 32.5%. nickel, up to 6% manganese, up to 10% molybdenum, up to 6% copper, and the balance essentially iron, the amounts of nickel, manganeses, molybdenum and copper in said reference alloy composition' being within their respective ranges such that the relationships expressed by the following equations:

are satisfied, 0g and 0,, being the Curie temperature and martensitic transformation temperature, respectively, of said reference alloy composition and A and A; being constants; and thereafter producing the iron-nickel temperature compensation alloy by the same method and with the same raw materials as employed in producing thefreference alloy, said temperature compensation alloy being characterized in that it contains not more than 0.03% carbon, not more than 0.03% silicon, 28.4% to 32.5% nickel, and, at least one metal selected from the groupconsisting of molybdenum and copper in the ranges of 1% .to 10% molybdenum and 0.6% to 6% copper, and ,upto 6% manganese, and being further characterizedin that the amounts of nickel, molybdenum, copper and manganese are present with their respective ranges suchthat the relationships expressed by the following equations: v

References Cited in the file of this patent UNITED STATES PATENTS 11,988,568 Randolph eta1 Jan. 27, 1935 2,719,084 Countis Sept. 27, 1955 2,720,603

Mitchell Oct. 11, 1955 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,930,725 March 29, 1960 Charles Alfred Clark It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 57, in the formula after "12" insert .a period; column 5, lines 54 and 55, for "impulity" read impurity line :56, after "that" insert the column 6, line 52, in the formula after "12" insert a comma; column 7, line 4, in the formula after "9" insert a comma; line 19, in the formula after "12" insert a comma; line 51 for "wtih" read with column 8, line 20, for "manganeses" read manganese line 41, for "with"' read within Signed and sealed this llth day of April 1961,

. (SEAL) Attest:

"ERNEST w. SWIDER ARTHUR w. CROCKER ttestmg Ocer Acting Commissioner of Patents 

1. A TEMPERATURE RESPONSIVE ELEMENT FOR USE IN MAGETIC INDICATING INSTRUMENTS SUBJECTED IN SERVICE TO CHANGES IN TEMPERATURE OVER A WIDE RANGE OF TEMPERATURE COMPRISED TO A TEMPERATURE COMPENSING ALLOY CHARACTERIZED BY THE PROPERTY OF HAVING A SPECIFIED CURIE TEMPRETURE AND MARTENSITIC TRANSFORMATION TEMPERATURE, SAID COMPENSATING ALLOY BEING SUBSTANTIALLY FREE OF CARBON AND SILICON AND CONTAINING 28.4% TO 32.5% NICKEL, AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF COPPER AND MOLYBDENUM IN AMOUNTS OF UP TO 6% COPPER AND UP TO 10% MOLYBDENUM, UP TO 6% MANGANESE AND THE BALANCE BEING SUBSTANTIALLY IRON, THE NICKEL AND METAL FROM THE GROUP CONSISTING OF COPPER AND MOLYBDENUM AND THE MANGANESE BEING PRESENT IN SUCH AMOUNTS AS TO SATISFY THE RELATIONSHIP EXPRESSED BY THE FORMULA 